The present invention relates to a method for the production of dimethyl ether (DME). DME can be used as a solvent and also as an intermediate in the synthesis of other compounds.
The method considered here is the dehydration of methanol using the so-called reactive distillation (RD) system. In an RD system both the production and purification of DME are performed simultaneously in one single reactor/distillation tower, which is technically entitled a reactive distillation column (Reactive Distillation Status and Future Directions, Sundmacher, Kai/Kienle, Achim, 1. Edition—December 2003, ISBN-13: 978-3-527-30579-7-Wiley-VCH, Weinheim).
The dehydration of methanol to produce DME through an RD system is disclosed, e.g., in the documents EP 407 038 A (Smith et al.) and U.S. Pat. No. 5,684,213 (Nemphos et al.).
EP 407 038 A discloses the application of a variety of acidic catalysts under different temperature and pressure conditions. In their work a stream of alkyl alcohols enters a middle section of the RD tower, where the reaction takes place over a catalyst bed and the separation is performed at the same time. The overhead comprising DME is condensed in a condenser and fed to an accumulator. The bottoms portion is primarily water. A reboiler is provided to recycle a portion of the bottom.
U.S. Pat. No. 5,684,213 suggests a process almost similar to that mentioned above with the exception that an H2 stream was used to increase the efficiency of the system. The operating conditions for a group of alkyl ethers were mentioned to be 130-300° C. and 140 to 6800 kPa.
The concentration of DME is controlled at the top of the tower by adjusting the reflux ratio, and at the bottom the temperature was controlled via adjusting the amount of “reboiled ratio” by controlling the amount of used steam.
U.S. Pat. No. 5,705,711 A refers to a process for the production of methyl tert.-butyl ether by dehydration of methanol and tert butanol. The process described in this patent application does not refer to the production of DME.
For determination of the optimum system design at any section of the RD tower the simultaneous consideration of the effects of operational and kinetic parameters is required. For example, adjusting the tower pressure involves changing the operational temperature of the tower. The same is true with regard to the conditions of the condenser, reboiler and their utilities. In previous works, a variety of operational temperatures and pressures, and the amount of the reflux ratio were addressed.
In using RD for the production of DME through the previously mentioned systems, the complex interaction of the effective factors is a drawback, and hence, any measures taken to simplify the system will be valuable.
In the control systems according to the art, the amount of the reflux stream is used to adjust the product concentration. The amount of the reboiled stream, which is controlled by the amount of steam used in the reboiler, is used to adjust the reaction bed temperature. Known RD tower control systems are complicated and hence expensive.
Due to different operating conditions and concentrations of liquid or gas phases, the combination of the prior art processes to produce dimethyl ether with processes for the production of methanol is highly complicated.
Furthermore, the methods according to the prior art consume high amounts of energy.